Field of the Invention
The present invention relates to a method of controlling the rate at which a stream of a product, consisting of a large plurality of individual portions or pieces, is fed by an upstream process that conditions the stream of product to a downstream process that either further conditions the stream of product or weighs and packages the stream of product. More specifically, the present invention relates to a method of harmonizing the control of the upstream process and an associated downstream process.
Background of the Related Art
Many products are mass produced in a facility with sequential processes to step-wise condition, weigh and package the products. An upstream process conditions the products and feeds a stream of conditioned products to a downstream process in which the products are either further conditioned or weighed and packaged. Automation of the processes may, if done correctly, maximize production and product quality.
Continuous operation of the downstream process at or near a desired rate setting requires that the upstream process must at least meet, and preferably slightly exceed, the demand rate for conditioned products required by the downstream process. This operational mode sustains the desired rate of product output. The downstream process can only process the conditioned products that are delivered by the upstream process. Given this dependent relationship between the downstream process and the upstream process, the harmonization of control of the facility requires that the upstream process be operated at a rate that meets or exceeds the demand requirement of the downstream process.
Those knowledgeable of control methods will understand that precisely matching the throughput rate of two independently-operated and sequential processes is extremely difficult. Either the rate of throughput of the downstream process will exceed the rate at which conditioned product is delivered by the upstream process, thus requiring occasional interruptions in the downstream process to allow the upstream process to “catch up,” or the rate at which conditioned product is delivered by the upstream process will exceed the rate at which the downstream process can accept and process conditioned product, thus requiring interruptions in the upstream process to prevent unwanted accumulation of conditioned product. In many processes, this latter mode of operation is problematic if stopping and restarting the upstream process results in a loss of quality control of the conditioned product produced by the upstream process. In this case, an operator using conventional control processes is put in the position of having to choose between achieving the desired rate of production and maintaining of the quality of the product. This conflict gives rise to the need for a control method that serves to automatically monitor performance indicating variables and equipment settings of the upstream and the downstream processes and to automatically adjust equipment settings to achieve the desired rate of production without sacrificing product quality.
There are many types of processes that include equipment that cannot be instantly stopped and later restarted without affecting the quality of the product being conditioned. For example, but not by way of limitation, if the upstream process includes the use of an electrical resistance heating element and the related application of heat to a stream of product by activation of the heating element, a time interval is required for the heating element to cool from the normal operating temperature to an inactive state. During this interval of “cooling time,” the portion of the product stream exposed to the heating element will continue to be heated at a diminishing rate of heat transfer after the electrical current to the heating element is interrupted. Similarly, upon restarting of the upstream process, the heating element requires a time interval to warm from an inactive state to a normal operating temperature. During this interval of time, the portion of the product stream exposed to the heating element will be heated at an increasing rate, but will initially be heated at a temperature that is substantially less than the normal operating temperature of the heating element until the heating elements reach the normal operating temperature. A portion of the product stream that is exposed to this interruption of conditioning by the heating element in the upstream process will be of a different quality than other portions of the product stream that are conditioned by the heating element operating at a steady state.
Another example of a scenario involving an upstream process that feeds conditioned product to a downstream process, and one in which the interruption of an upstream process impairs the quality of a portion of the stream of product, involves the application of a sprinkled or sprayed additive material to the stream of product. The sprinkled or sprayed material may be a coating or a flavoring agent, such as a seasoning material. For example, but not by way of limitation, a stream of product consisting of a large plurality of individual food portions may be conditioned in an upstream process by controlled application of a seasoning material. During steady state operation of the upstream process, the seasoning material is dispensed at a controlled rate—that yields optimal results—onto a product stream moving underneath a seasoning dispenser. As with the heating element in the prior example, stopping and restarting the seasoning material dispenser of the upstream process impairs the quality of the portion of the product stream that is below the seasoning dispenser at the time at which the dispenser is stopped and then later restarted. The rate at which the seasoning material is applied to that affected portion of the product stream will vary, and quality will be compromised. Too little seasoning material per unit of the seasoned product or too much seasoning material per unit of the seasoned product will result in an unwanted variance of flavor of the product and an undesirable loss of consumer satisfaction.
What is needed is a control method for efficiently operating an upstream process, that conditions a stream of product, and a downstream process, that receives and either further processes the conditioned product stream from the upstream process or weighs and packages the conditioned product stream from the upstream process, and where the upstream process is one in which interruptions in conditioning operation impairs product quality and the downstream process is one in which interruptions in operation impairs the rate of production.